Radiation therapy is widely used for the treatment of tumors. A course of radiation therapy typically includes a planning session and one or more treatment sessions. During the planning session, an oncologist obtains information describing the nature, location, size, and shape of the tumor. Based on the information, the oncologist develops a treatment plan that includes such parameters as radiation beam energy, radiation dose, treatment duration, etc. The treatment plan is executed during the treatment sessions.
In an intensity modulated radiation therapy (IMRT), the radiation intensity projected onto different parts of the tumor can be adjusted according to the treatment plan. The intensity modulation enables the oncologist to adjust the radiation dose received by different parts of the patient's body. Using IMRT, the oncologist can deliver a high radiation dose to the tumor, thereby increasing the therapy efficiency and reducing the inadvertent radiation exposure of the healthy tissues surrounding the tumor.
During a treatment session, the tumor may move due to the breathing or gastric and intestinal movements of the patient. Breathing motion momentarily and repeatedly causes the tumor to move out of the radiation beam and subjects the healthy tissues surrounding the tumor to the radiation. Training the patient for proper breathing techniques may reduce, but not eliminate, the movement of some tumors. The physiological gating of the radiation beam during the treatment session may also reduce the radiation exposure of the healthy tissues by switching off the radiation beam when the tumor moves out of the projected area of the radiation beam. In one gating process, the movement of the tumor is approximated as sinusoidal with a frequency equal to the inhale/exhale frequency of the patient. In another gating process, markers are placed on patient's thorax and/or abdomen to facilitate the detection of patient breathing and/or gastric and intestinal movements. Although the physiological gating process can reduce the radiation exposure of the tissues surrounding the tumor, it may prolong the duration of the treatment session by periodically switching off the radiation beam. This may reduce the throughput of the radiation therapy.
According, it would be advantageous to have an apparatus and a method for tracking the tumor movement during a radiation treatment therapy. It would also be advantageous for the apparatus and the method to be able to adjust the radiation beam in response to the tumor movement. It would be of further advantage if the apparatus can be made by modifying an existing radiation therapy apparatus.